When you design a species based on a single character, and you make that species so restrictive that creating that character is impossible, you shouldn’t design a whole sub-class just to allow that character. You should go back to the drawing board.
What possible reason is there to deny saurials the right to be paladins? Gods are racist.
The Complete Book of Humanoids Chapter 3: Humanoid Kits
After the unsettling hints of racism in the past subsection, we now have... even more overt racism! Humanoid wizards are rare because most humanoid races don't possess traditions of formal magical instruction, or even literacy, and/or they actively shun arcane magic as "evil". Most humanoid wizards have had to leave their tribes to pursue magic and complete their studies in a somewhat more welcoming environment.
All humanoid wizards are Generalists, according to this chapter, although I think that several of the races in Chapter 2 actually gave explicit statements otherwise. It's the shortest subchapter, with only three kits to examine; the Hedge Wizard, the Humanoid Scholar, and the Outlaw Mage.
Hedge wizards are the most common form of humanoid mage; hermits or social outcasts who have taught themselves arcane skills through study mixed with lots of trial and error; they gravitate towards the arts of alchemy, which mesh most readily with their focus on exploring the inherent magical properties of the world around them and the planes. Though they often develop fearsome reputations, their ability to provide knowledge, counsel and various alchemical conconctions keeps them too useful to be driven away.
The hedge wizard requires a minimum of Intelligence 9. It gains access to Herbalism as a bonus proficiency, and can attempt to brew up an antidote to poisoning in a process that takes a day and has a 25% + 5% per wizard level chance of successfully nullifying any potion. From 7th level onwards, they can also brew magical potions, using the rules from DMG. The downside is that their available schools of magic are severely restricted; a hedge wizard can only cast spells from the Abjuration, Conjuration, Divination and Enchantment schools - as well as one bonus school taken from either Illusion or Necromancy.
Remember that bit I touched upon about humanoid mages often leaving their birthplaces to seek out magical lore they can't gain access to in their own culture? Well, that's basically what this kit revolves around. Humanoid scholars are fascinated by the potential to learn, and so they leave their homes behind to explore, avidly seeking out knowledge wherever they might find it. Though they tend to be more focused on getting knowledge when young, older Scholars become surprisingly good teachers. They are usually not violent, but they are passionate about the pursuit of knowledge, which is their main reason for joining adventuring parties.
There is one racist line here about how scholars are rare because few humanoids have the patience or desire to learn more than they need to know to survive, but for the most part this is actually a very a positively described kit, focusing on how avidly devoted these mages are to learning as much as they can, whether it directly relates to spellcasting or not.
This kit is open to centaurs, fremlins, minotaurs, mongrelfolk, oni (ogre magi), and saurials, and requires Wisdom 11 and proficency in Ancient or Local History. They gain Reading/Writing and two nonweapon proficiencies from the list below as bonus proficiencies. However, their focus on learning over combat means that a humanoid scholar may only spend a single proficiency point on a weapon at character creation; the other points must be spent on, and I quote, "skills relating to the pursuit of knowledge". Also, they are forbidden from taking the skills Blind-fighting, Close-quarter Fighting, Running, and Wild Fighting.
The recommended skills, which the scholar gains the aforementioned two points in for free at first level, are:
The Outlaw Mage has either decided to use magic to supplement their ability to profit outside of the lore, or has turned to roguecraft in order to assist it in gaining access to magical lore and items it wouldn't be able to get legitimately. Regardless of whether the purpose is profit or to supplement their studies, the outlaw mage has learned they can survive and become rich by combining illusion, deception, and spellcraft. Outlaw mages can be selfless or selfish, but they are keenly aware that they are generally less adept at fighting than they are at sneaking or thinking; if an outlaw mage can't win through magic, thievery or wits, they will usually make a strategic retreat.
While not all outlaw mages are evil, they all operate outside of the laws of the land, and are willing to work alongside anyone who seems like they can profit them; an outlaw mage will as happily lead a gang of bandits or serve as an apprentice to an evil wizard as they will join a band of adventurers who feel the outlaw mage's combination of wizardry and roguish talents are useful to their goal.
...Basically, it's a whole kit dedicated to the concept of the multiclassed mage/thief, and I don't really get why this is a thing in the first place.
The kit is only open to Non-Good centaurs, fremlins, voadkyn, minotaurs, mongrelfolk, oni (ogre magi) and saurials with at least 9 Dexterity. They gain Hiding as a bonus proficiency, can learn to speak Thieves Cant, and can take rogue proficiencies without spending an extra slot. Their only hindrances are that they can't take the blind-fighting, close-quarter fighting, natural fighting and wild fighting proficiencies.
Well, it's not as bad as the Warrior Kits in terms of being uncomfortable or pointless, but I definitely have to call this out as pretty damn bland. The flavor on the kits is better than their Warrior counterparts, but at the same time, they just feel so pointless; the Outlaw Mage is literally a less XP-heavy mage/thief, the Humanoid Scholar could be literally any of the "Sagacious Archetype" wizard kits in other sourcebooks, and the Hedge Mage... well, alright, this actually does fit its namesake well, and it does mesh with the humanoid monoculture of this book, but I can just as easily see this being seen amongst humans or halflings as I can amongst orcs or goblins.
the Humanoid Scholar could be literally any of the "Sagacious Archetype" wizard kits in other sourcebooks, and the Hedge Mage... well, alright, this actually does fit its namesake well, and it does mesh with the humanoid monoculture of this book, but I can just as easily see this being seen amongst humans or halflings as I can amongst orcs or goblins.
The defining difference for orcs and goblins over humans and halflings (well, this is AD&D, so Halfling wizards aren't much of a thing either) is that both the culture the aspiring humanoid mage, and the civilized cultures which have most of the opportunities to learn magic, do not expect anyone from the humanoid races to want to be a mage, much less have the skill or dedication. Excelling despite these setbacks would be a defining feature. They could have leaned into that more, although I kinda fear what the result would have been.
I think there was a strong AD&D-era sentiment that Paladin-hood was a 'human' thing. The Saurials got a pass (of sorts) because they were the humans of their homeworld.
The Dragonlance Monstrous Compendium Appendix had a rare break from this as Dwarves were allowed to be Paladins (but that setting restricted Knights to be human only... Maybe half-elves, since one canonically got knighted for ceremonial reasons).
it's interesting that I feel like removing the Human requirement for paladin has been taken pretty well and is quite common. Perhaps Paladin no longer being a Special Super Class for those that rolled really well factors in. I feel like there's still more sentiments opposing Dwarf Wizards than Nonhuman Paladins.
Human only Paladins is entirely a relic of Gygaxian humanocentrism. Dwarves aren't Wizards (or at least not the same way) has a lot more currency in non-D&D media. There's lots of 'dwarves make magic items with runes and crafts but don't cast spells' going about in fantasy. Damnded if I know why, might even be principally a legacy of D&D that took harder, but there it is.
The Paladin class was, pre-3e, generally restricted to all but Humans. There were exceptions (Dragonlance Dwarves, as I said; Various others as well) but that was the general rule.
I think it was mainly an attempt to reinforce the idea that humans were competitive with others if not, as Raveled
says, dominant. Humans get special multiclassing, easy advancement, and not much else to make up for lack of special vision and similar.